Power brake booster with no-power operational features

ABSTRACT

A master cylinder assembly has a secondary piston assembly and a primary piston assembly mounted in a common bore to provide a primary pressurizing chamber between the piston assemblies and a secondary primary chamber between the secondary piston assembly and one end of the bore. The primary piston assembly is composed of two concentric pistons, one extending through a bore in the other. Two input members are provided, one of which is arranged to move both primary pistons concentrically under brake booster power to actuate the master cylinder, and the other of which is arranged to move only one of the primary pistons, without moving the other, to actuate the master cylinder manually when no power assist is available from the booster. The booster assembly is actuated through a manually moved push rod which in turn permits movement of a valve input member forming a part of the booster control valve assembly. The valve input member is arranged so that it normally follows movement of the push rod but is not positively attached thereto. A reaction system in the booster provides for booster &#39;&#39;&#39;&#39;feel&#39;&#39;&#39;&#39; to be transmitted to the input push rod. The booster control valve assembly is mounted in the booster power wall. The power wall includes one or more power diaphragms and is actuated by differential pressures imposed on opposite sides of the diaphragms under control of the control valve assembly. The power wall is connected to move the master cylinder input means which actuates both primary pistons, and is so arranged as to permit movement of the other master cylinder input means without requiring movement of the power wall when no booster assist force is available.

United States Patent Nordeen Nov. 13, 1973 POWER BRAKE BOOSTER WITHNO-POWER OPERATIONAL FEATURES- [75] Inventor: Donald L. Nordeen, EastLansing,

Mich.

[73] Assignee: General Motors Corporation,

Detroit, Mich.

[22] Filed: May 31, 1972 [21] Appl. No.: 258,249

[52] U.S. Cl 60/550, 60/553, 91/391 R, 137/6275 [51] Int. Cl. F151)7/08, F15b 13/10 [58] Field of Search 60/54.5 P, 54.6 P, 60/54.6 E, 550,553; 91/391 R; 137/6275 [56] References Cited UNITED STATES PATENTS3,559,406 2/1971 Gardner 60/54.5 P 3,473,329 10/1969 Eggstein (SO/54.6 P3,422,622 l/l9 69 Arentoft et al 60/54.6 P 3,540,219 11/1970 l-luruta etal. 60/54.6 P 3,162,018 12/1964 Daley 60/54.6 P

571 ABSTRACT A master cylinder assembly has a secondary piston assemblyand a primary piston assembly mounted in a common bore to provide aprimary pressurizing chamber between the piston assemblies and asecondary primary chamber between the secondary piston assembly and oneend of the bore. The primary piston assembly is composed of twoconcentric pistons, one extending through a bore in the other. Two inputmembers are provided, one of which is arranged to move both primarypistons concentrically under brake booster power to actuate the mastercylinder, and the other of which is arranged to move only one of theprimary pistons, without moving the other, to actuate the mastercylinder manually when no power assist is available from the booster.The booster assembly is actuated through a manually moved push rod whichin turn permits movement of a valve input member forming a part of thebooster control valve assembly. The valve input member is arranged sothat it normally follows movement of the push rod but is not positivelyattached thereto. A reaction system in the booster provides for boosterfeel" to be transmitted to the input push rod. The booster control valveassembly is mounted in the booster power wall. The power wall includesone or more power diaphragms and is actuated by differential pressuresimposed on opposite sides of the diaphragms under control of the controlvalve assembly. The power wall is connected to move the master cylinderinput means which actuates both primary pistons, and is so arranged asto permit movement of the other master cylinder input means withoutrequiring movement of the power wall when no booster assist force isavailable.

1 Claim, 3 Drawing Figures POWER BRAKE BOOSTER WITH NO-POWER OPERATIONALFEATURES It is common to provide a brake system with a master cylinderhaving manual pressurizing chambers so that the brake system is dividedinto two or more fluidly independent brake pressurizing circuits. It isalso common to actuate such master cylinders through a power brakebooster in order to maintain high level of brake pressurization withoutrequiring high levels of brake pedal pressure or pedal movement undernormal operating conditions. The brake booster may be poweredpneumatically or hydraulically, it being most common at this time to usea vacuum-atmospheric brake booster in automotive vehicles. In someinstances, particularly in trucks, an atomspheric-super-atmospheric airpressure system is used, and in other instances, a hydraulicallypressure actuated system is used. In all of these arrangements, anoutside power source is depended upon to obtain the power assistingaction of the brake booster. The booster can at times have insufficientoutside power supplied to it so as to reduce or eliminate the powerassist available. While brake boosters in master cylinder assemblies canalso be normally actuated manually, there will of necessity be reducedbrake effectiveness since less total force is available to actuate themaster cylinder.

Different arrangements and proposals are known which will tend toimprove the brake effectiveness under such circumstances. It isdesirable to accomplish this insofar as possible without requiring achange in the normal brake pedal height, and the normal operation of thebrake system should not be materially affected. The manually operatedsystem should be utilized any time there is insufficient power assistand, at the same time, the normal braking operation should not beaffected. ln order to obtain these goals, and to provide a reasonablebrake system with reduced or nopower assist, the braking system isdesigned so that normal stops can be made with reasonable pedal forceexerted by the vehicle operator.

In the preferred embodiment herein disclosed and utilizing the inventionto which the claims are directed, increased brake effectiveness isobtained by changing the mechanical advantage between the brake pedaland the master cylinder hydraulic pressure by providing two primarypistons in the master cylinder, and by providing a power brake boosterwhich is arranged to normally actuate both primary pistons. However, ifa loss of power assistance occurs, the booster is arranged to actuateonly one of the primary pistons. This has the effect of changing thebrake pedal ratio when power assist is not available and results in agreater hydraulic pressure output per unit of brake pedal apply force.The brake booster is also arranged to apply the brake pedal forcethrough the brake pedal push rod directly to the master cylinder so thatthe booster power wall does not have to be displaced. The inventionherein claimed is directed to the brake booster portion of the boosterand master cylinder assembly.

IN THE DRAWING FIG. 1 is a cross section view of a brake booster andmaster cylinder assembly embodying the invention.

FIG. 2 is a cross section view ofa portion of the master cylinderassembly of FIG. 1, taken in the direction of arrows 2-2 of that figure.

FIG. 3 is an enlarged view of the brake booster control valve mechanismof FIG. 1.

The brake booster and master cylinder assembly 10 includes a boosterassembly 12 and a master cylinder assembly 14. The booster assembly isillustrated as being a vacuum suspended-type booster similar to thosecurrently used in production automobiles. It has a housing 16 providedwith a rear wall 18, a front wall 20 and an intermediate wall 22. Powerwall means 24 is contained within the booster housing 16 and includesthe power piston 26 and diaphragms 28 and 30. The inner peripheries ofthe diaphragms are sealingly connected to the power piston 26 and to thehousing 16, with the diaphragms being positioned in the housing onopposite sides of intermediate wall 22. The housing walls and diaphragmstherefore divide the housing into chambers 32, 34, 36 and 38. Chambers34 and 38 are interconnected and normally impressed with vacuum from asuitable vacuum sourceyas is well known in the art. When the booster isin the released position, chambers 32 and 36 are also impressed withvacuum. When the booster is actuated, as described below, atmosphericpressure is controllably admitted to chambers 32 and 36, causing thediaphragms and power piston to move leftwardly, as seen in FIG. 1, toactuate master cylinder assembly 14.

The power piston 26 has a rearwardly extending section 40 which extendsout of the housing wall 18 and may be suitably covered by a boot 42.Section 40 has the booster control valve assembly 44 received therein.This valve assembly includes the vacuum valve seat 46, which isannularly formed as a part of piston 26, the valve member 48 mounted insection 40 for axial reciprocal movement relative to seat 46 and urgedtoward that seat by spring 50, and the valve input member 52. This inputmember is reciprocably mounted concentrically within the valve seat 46and is formed to provide the air valve seat 54. This general arrangementis well known in the art and the manner of operation is likewise so wellknown as to only require a general description. In the normal releasedposition, valve seat 54 engages valve member 48 and'holds it away fromvalve seat 46 so that vacuum is supplied to all of the booster chambers32, 34, 36 and 38. When the valve input member is moved leftwardly,valve member 48 follows .until it engages vacuum valve seat 46, thusclosing the vacuum connection to chambers 32 and 36. Further movement ofthe valve input member 52 moves valve seat 54 away from valve member 48,admitting air under atmospheric pressure to chambers 32 and 36. Thepressure differentials acting on diaphragms 28 and 30 and on piston 26cause the power wall assembly to move leftwardly against the boosterpiston return spring 56. Since the valve seat 46 and the valve member 48are mounted in the piston section 40, they also move leftwardly relativeto the valve input member 52. The valve member 48 therefore reengagesthe air valve seat 54, closing off the air pressure connection tochambers 32 and 36. When valve member 48 engages both seats 46 and54,'the'valve assembly is in the poised position, holding in the boosterthe required pressure differential to maintain this position. Upon brakerelease, the valve input member 52 is moved rightwardly relative topiston 26, removing valve member 48 from the vacuum valve seat 46,thereby decreasing the pressure differential across diaphragms 28 and 30and permitting rightward movement of the power wall means under theforce of booster return spring 56. To this extent, the booster operatesin the same manner as boosters currently used.

The booster valve input member 52 is engaged by an annular springretainer 58 on its rightward end, the spring retainer beingconcentrically within and spaced from the valve member 48. The springretainer is formed at the end opposite the valve input member 52 toprovide a spring seat 60. Another spring seat 62, which may be a snapring, is provided in the outer end of piston section 40 and acompression spring 64 is seated on seats 60 and 62 so as to urge springretainer 58 leftwardly. Since the leftward end of the spring retainer 58engages valve input member 52, the valve input member is also urgedleftwardly. It is provided with a snap ring on another stop member 66which can engage one side of shoulder 70 on piston 26 to limit itsleftward movement relative to piston 26. Valve input member 52 isprovided with another snap ring or stop member 68 on the opposite sideof the piston shoulder 70, so as to limit rightward movement of thevalve input member relative to the piston 26. Thus, shoulder 70 ispositioned between snap rings 66 and 68 and limits valve input movementbeyond a predetermined amount.

The push rod 72 is suitably connected at one end, not shown, to thebrake pedal so as to be movable leftwardly under brake pedal actuatingforce exerted manually by the vehicle operator. The other end of pushrod 72 is suitably connected, as by a ball and socket pivot joint, to aforce transmission member 74. Member 74 is reciprocably received in abore 76 formed in piston 26. The right end of member 74 adjacent theball and socket joint has a shoulder 78 which mates with a shoulder 80formed interiorly of the valve input member 52. The valve input memberis generally annular in form so that the push rod 72 and the member 74extend therethrough. Other than the abutting engagement of shoulder 78and 80, there is no direct mechanical force transmitting connectionbetween the valve input member 52 and the push rod 72 with its member74. It can be seen that the shoulder engaging connection is maintained,within limits established by snap rings 66 and 68 and piston shoulder70, by the force'of spring 64 acting on the valve input member throughspring retainer 58. Thus, the valve input'member 52 will follow themanual input movements of the push rod 72 to control the brake booster.

The leftward end of piston bore 76 has an enlarged section 82 joiningthe other portion of the bore at shoulder 84. A power force transmissionoutput member 86 is reciprocably received within bore section 82 and isgenerally tubular in form so as to have a cylinder wall 88 interiorlythereof. The right end 90 of output member 86 is engageable withshoulder 84 for transmission of brake booster generated force in aleftward direction. The left end 92 of output member 86 forms a mastercylinder input member and is arranged to actuate the master cylinderassembly 14 in a manner to be described. A reaction disc 94, suitablyformed of a rubber-like material, is received within the cylinder wall88 of member 86 adjacent output member end 90 so that its outerperiphery engages the cylinder wall 88, one side engages shoulder 84,and the other side is engaged by a movable cup 96 which is reciprocablymounted within the cylinder wall 88. The disc 94 and cup 96 are axiallyapertured so that a reduced diameter extension 98 of the forcetransmission member 74 extends therethrough from a shoulder 100 ofmember 74. Extension 98 has a spring seat 102 mounted on its leftwardend within cup 96 and supporting the right end of compression spring104. A piston-like output member 106 is reciprocably received within thecylinder wall 88 and the left end of spring 104 is seated against it.The left end 108 of output member 106 engages a bifurcated mastercylinder input member 110, which is reciprocably received within theleft end 92 of member 86. Bifurcated member 110 has two legs 112 and114, better seen in FIG. 2, which are in cross section preferably formedas arcuate portions, located in diametrically opposed relation.

The master cylinder assembly 14 includes a housing 116 having brakefluid reservoirs 118 and 120 respectively connected through compensationports 122 and 124 with bore 126. The right or rear end 128 of housing116 issuitably secured to the wall 20 of the brake booster assembly andthe open end of the bore 126 extending through end 128 is aligned toreceive the master cylinder input members formed by left end 92 ofmember 86 and the bifurcated member 110. A secondary pressurizing pistonassembly 130 is reciprocably received in the forward end of bore 126 andis normally axially spaced from the bore end 132 to form within the borethe secondary pressurizing chamber 134. A primary pressurizing pistonassembly 136 is reciprocably received in the rear end of bore 126 inaxial alignment with piston assembly 130 and is normally spaced frompiston assembly 130 to form the primary pressurizing chamber 138 in thebore between the two piston assemblies. A piston stop in the form ofsnap ring 140 is inserted in the rear end of the bore 126 to provide arearward stop for piston assembly 136. Piston return springs 142 and 144are respectively positioned in chambers 134 and 138 and, as will befurther described, cooperate to hold piston assembly 136 in abuttingrelation with stop 140 when the master cylinder is not actuated andthereby precisely position both piston assemblies so that compensationport 122 is open to chamber 138 and compensation port 124 is open tochamber 134.

Piston assembly 130 includes a piston 146, which is generallyspool-shaped. The forward piston land 148 has a piston cup 150 engagingthe forward end thereof and also acting as a valve to close compensationport 124 when the piston is moved in the pressurizing direction. Anaxially positioned piston extension 152 extends forwardly of land 148and the extension end 154 is aligned for engagement with bore end 132after a predetermined amount of forward movement of the piston. A springseat 156 is mounted on extension 152 and receives one end of pistonreturn spring 142. The other end of spring 142 engages bore end 132. Therear land 158 of piston 146 has oppositely directed V-block seals 160and 162 thereon which effectively seal the chambers on both sides ofland 158. A rearwardly extending boss 164 is provided on the rear faceof land 158 and is sufficiently smaller in diameter to permit the springretainer 166 to have its annular forward end 167 engage the annularsurface of land 158. The retainer forward end 167 is flanged to providea seat for the forward end of piston return spring 144. The forward end167 of retainer 166 is pressed against the annular surface of land 158but is not otherwise connected thereto to permit leftward movement ofthe secondary piston 146 without a corresponding movement of saidretainer 166. The retainer 166 and spring 144 are considered to be partsof the primary piston assembly 136, and are located in chamber 138.

Piston assembly 136 includes a first primary piston 168, which isgenerally spool-shaped and provided with a front land 170 and a rearland 172. Cup-like seals 174 and 176 are respectively provided on lands170 and 172 to seal with a bore 126. Piston 168 has a bore 178 extendingaxially therethrough so as to reciprocably receive the second primarypiston 180. Thus the two primary pistons are concentrically mounted. Aseal 182 is provided between the two pistons to seal bore 178.

The rear end 184 of piston 180 extends out of bore 178 past the firstprimary piston rear land 172 and has secured thereto a plate member 186.The plate member is of substantially the same diameter as piston land172 and is axially positioned between that land and piston stop 140. Theplate member is apertured or otherwise suitably formed to provideaxially extending openings therethrough which are positioned radiallyoutward of the end 184 of piston 180 so that the apertures are in axialalignment with at least portions of the rear face 188 of land 172. Inthe particular construction shown in the drawing, plate member 186 isshaped somewhat like a butterfly or bow tie, as seen in FIG. 2. Theapertures in this instance are formed at 190 and 192 by the arcuatelyomitted portions of the plate member. The apertures are so arranged thatthe bifurcated member legs 112 and 114 respectively extend through theapertures with their forward ends engaging the rear face 188 of piston168, but not engaging, in axial force transmitting relation, the platemember 186 or piston 180.

The forward end 92 of member 86 abuts the rear face 194 of plate member186 in axial force transmitting relationship so that when brake applyforce is transmitted through member 86, it passes through plate member186 to both pistons 168 and 180, moving them concurrently in a forwarddirection away from stop 140. However, if brake actuating force istransmitted only through the bifurcated member 110, only piston 168 ismoved forwardly, leaving plate member 186 in position against stop 140and affording no movement of piston 180.

The forward end 196 of piston 180 has a stop 198 thereon in the formof'a snap ring, the piston end and snap ring being located in chamber138. The rear end 200 of spring retainer 166 is recieved over snap ring198 and inwardly flanged to normally rest against the snap ring when themaster cylinder is in the released position. Thus, spring 144 is cagedbetween spring seat 167 and the forward face of piston land 170, whichprovides a spring seat for the rear end of spring 144. The inwardlyflanged end 200 of spring retainer 166 is slidably mounted relative topiston 180 so that some relative movement can occur. Under certainconditions of operation, such as when the master cylinder is actuatedbut no pressure is generated in chamber 138, piston 168 can moveforwardly against spring 144 until the forward face of the pistonengages the spring retainer end 200. This will result in a mechanicalforce transmitting connection through abutting surfaces to move pistonassembly 130 forwardly even though no pressure is generated in chamber138. If this occurs under power boost actuation, piston 180 will movewith piston 168.

In normal brake operation, with the primary pressurizing chamber 138connected to one brake circuit and the secondary pressurizing chamber134 connected to the other brake circuit, both brake circuits will bepressurized in response to forward manual movement of push rod 72 whenthe vehicle operator actuates the brake pedal. This movement of push rod72 moves force transmission member 74 forwardly, actuating the valveassembly 44 as earlier described, and also slightly compressing spring104. The shoulder of force transmitting member 72 will engage the innerportion of reaction disc 94 and shoulder 84 of the power piston 26 willengage the outer portion of the reaction disc and the rear end of member86. The power brake apply force which moves piston 26 leftwardly istransmitted primarily through member 86 to move both primary pistons 168and 180 in the forward, fluid pressurizing, direction. Some of the powerapply force is also transmitted through reaction disc 94 and cup 96 tooutput member 106 and bifurcated member 110 to exert some powergenerated force directly on piston 168. Reaction to this force will bereturned through the reaction disc and a portion thereof exerted throughthe inner portion of disc 94 against force transmission member 74 to thepush rod 72 to provide feel to the brake pedal. With both primarypistons moving leftwardly, force is also transmitted through spring 144to move piston assembly leftwardly. Cups and 174 respectively covercompensation ports 122 and 124, and further leftward movementpressurizes fluid in chambers 134 and 138, actuating the brakes.

If the brakes are applied and no booster power is sembly 44 to operateas before. However, with no pressure differential imposed thereon, thepower wall of the booster will not be moved against the return spring56. Piston 26 will not be axially moved and, therefore, member 86 willnot be axially moved. Since movement of member 86 is necessary to moveplate member 186 and piston 180, those elements will not be movedaxially. However, the manually exerted force transmitted through member74 will pass through reaction disc 94 after shoulder 100 engages it, andcup 96 will be moved leftwardly. This will in turn move member 106leftwardly, causing the bifurcated master cylinder input member 110 tobe moved leftwardly. Since the bifurcated ends only engage piston 168,this leftward movement will result in movement only of primary piston168, closing compensation port 22 and then commencing to pressurizefluid in chamber 138.

Since the effective area of the primary piston assembly is now smaller,a greater hydraulic pressure for a given input force will result. Whilethis pressure will be lower in terms of brake pedal stroke, it will begreater than would be the case if the primary piston assembly had thesame effective area at all times. This relatively high hydraulicpressure will be generated in both pressurizing chambers 138 and 134because of the balancing action of the secondary piston assembly causedby leftward movement of the secondary piston 146 away from the end 167of retainer 166 in response to increased pressurization of fluid withinthe pressurizing chamber 138. The booster piston return spring 56 neednot be manually overcome. It is for this reason that the valve inputmember 52 is not mechanically fastened to the push rod 72 or member 74.As can be seen, the arrangement permits the push rod 72 to manually movemember 74 away from the valve input member, separating shoulders 78 and80, after snap ring 66 engages shoulder 70. This will also occur uponbooster run-out when there is insufficient pressure differential tofully actuate the assembly.

Since there is no secured connection between the booster input and thevalve, the preload forces on the various springs in the system must becarefully controlled to insure proper operation. The booster returnspring is required so that the booster is fully returned when the brakesare not applied. Piston return spring 142 acts through the pistonassemblies, including spring 144, and then through the booster outputmembers and the force transmission member 74 to move valve input member52 rightwardly against the force of spring 64 and to also move the pushrod 72 to the brake release position. In order to accomplish this, andto insure the proper relationship between the master cylinder pistonassemblies, the preload on spring 144 must be greater than the forcefrom spring 142. Spring 104 also acts to insure the full return of valveinput member 52 and valve 48. Therefore, the preload force on spring 104is greater than the preload force on spring 64 but is less than thepreload force of spring 142. Springs 64 and 104 insure direct mechanicalcontact between transmission member shoulder 78 and valve input membershoulder 80 unless there is a loss of brake booster power. There is alsosufficient clearance pro vided between the booster piston 26 and themember 86 so that the displacement required in the reaction disc 94 tobalance the booster valve can be obtained for all power operatingconditions. The area ratio between primary pistons 168 and 180 isselected so that the change in pedal displacement in the event of lossof booster power is within an acceptable range. At the same time, theremust be sufficient difference in the areas of these pistons to achievethe desired amount of reduced pedal effort under this circumstance.

What is claimed is:

l. A power brake assembly comprising:

a master cylinder assembly having pressurizing piston means thereinincluding a first primary piston and a second primary piston acting whenactuated to pressure fluid in a primary pressurizing chamber,

said valve means including an input member slidably mounted on saidmanual force input means and having a shoulder mating with said locatingshoulder and a locating spring acting between said power wall means andsaid input member and normally holding said valve input member shoulderin direct mechanical contact with said locating shoulder to cause saidinput member to follow movements of said manual force input means, thepreload on said locating spring being less than the preload on saidpiston return spring;

valve seat means formed on said input member and said power wall means,a valve movably mounted in said power wall means and cooperating withsaid valve seat means to control said booster, stop means between saidpower wall means and said input member limiting relative movement ofsaid input member relative to said power wall means upon a predeterminedamount of movement of said manual force input means relative to saidpower wall means in the master cylinder actuating direction; and

reaction means for transmitting reaction forces between said power wallmeans and said first and second force output means and between saidsecond force output means and said manual force input means, saidreaction means including a reaction spring between said second forceoutput means and said manual force input means having a prelaodintermediate the preloads of said piston return spring and said locatingspring.

1. A power brake assembly comprising: a master cylinder assembly havingpressurizing piston means therein including a first primary piston and asecond primary piston acting when actuated to pressure fluid in aprimary pressurizing chamber, piston return stop means, and a pistonreturn spring having a first spring preload and operatively acting onsaid primary pistons to position same against said stop means when themaster cylinder assembly is not actuated; a brake booster assemblyhaving power wall means, first and second force output means, manualforce input means reciprocably mounted in said power wall means andhaving a locating shoulder thereon, and booster control vavle means insaid power wall means and operatively controlled by movement of saidmanual force input means; said valve means including an input memberslidably mounted on said manual force input means and having a shouldermating with said locating shoulder and a locating spring acting betweensaid power wall means and said input member and normally holding saidvalve input member shoulder in direct mechanical contact with saidlocating shoulder to cause said input member to follow movements of saidmanual force input means, the preload on said locating spring being lessthan the preload on said piston return spring; valve seat means formedon said input member and said power wall means, a valve movably mountedin said power wall means and cooperating with said valve seat means tocontrol said booster, stop means between said power wall means and saidinput member limiting relative movement of said input member relative tosaid power wall means upon a predetermined amount of movement of saidmanual force input means relative to said power wall means in the mastercylinder actuating direction; and reaction means for transmittingreaction forces between said power wall means and said first and secondforce output means and between said second force output means and saidmanual force input means, said reaction means including a reactionspring between said second force output means and said manual forceinput means having a prelaod intermediate the preloads of said pistonreturn spring and said locating spring.